1. Technical Field
The present disclosure relates to an optical filter which obtains both of a color image and a polarized light image at the same time, and relates to a polarization imaging device which uses the filter.
2. Description of the Related Art
In recent years, an imaging element (polarization imaging device) which obtains a color image and a polarized light image at the same time has been required in the fields of examination endoscopes, stereoscopic imaging cameras, on-vehicle cameras, and the like. If polarized light information is obtained in addition to color image information, halation can be removed from reflected light. In addition, if polarized light information is obtained, the normal line direction of a surface of an object can be estimated; thus, surface irregularity and a flaw of the object can be detected, and spilled water and an obstacle on a road surface can be detected. Further, by using a polarization imaging device in combination with a polarized illumination, if an object is a semi-transparent mucus membrane, the information of the surface structure of the mucus membrane can be obtained. In order to realize these functions, an imaging device equipped with a polarizer is necessary. As the polarizer, a wire grid polarizer, which polarizes light in a wide visible light region, is effectively used.
U.S. Pat. No. 8,759,742 and U.S. Patent Application Publication No. 2012/0319222 disclose that, in order to obtain a color image and a polarized light image at the same time, on an upper layer or a lower layer of a conventional color solid-state image sensor is formed a mosaic array in which wire grid polarizers in different directions are combined with each other.